Due to a lack of engineering experience, research on ground deformation during shield machine tunneling in sludge layers is limited, especially in areas with plastic drainage plates installed for ...ground stabilization. When the shield passes through this area, the shield cutterhead may be jammed by the drainage plates, resulting in excavation surface instability, excess ground deformation, and schedule delay. In this work, a Mindlin solution for ground deformation in such a layer is obtained, considering four factors: the frontal additional pressure generated by the shield cutterhead due to the soil squeezing effect, the uneven lateral friction between the shield shell and the soil, the frontal friction generated by the shield cutterhead when cutting through the drainage plate, and the shield machine restart after shutdown. The results show that the theoretical curve is in good agreement with the measured values. The maximum settlement was approximately 10 m behind the excavation surface, and the maximum uplift was approximately 5 m in front of the excavation surface. The most influential factor among all the studied factors was the additional pressure on the shield cutter, which accounted for approximately 56% of the maximum settlement and 60% of the maximum uplift. The soil settlement mainly occurred within 12 m on both sides of the tunnel axis. The maximum settlements at the different soil depths tested were all directly below the tunnel axis.
The construction of urban cross-river tunnels usually requires passing under river embankments, which inevitably disturbs the embankment substratum and causes ground deformation. Previous engineering ...cases have shown that embankment settlement is greater than ordinary surface settlement and that uneven settlement results in cracks of in the embankment, reducing the embankment stability. Based on a cross-river tunnel project in China, the construction risks caused by the additional stress on the embankment substratum, asymmetrical embankment load, and shield tunneling in saturated fine sand are analyzed during a large-diameter slurry shield tunneling below an urban river embankment diagonally. Additionally, relevant risk control measures, such as slurry pressure, jacking thrust setting, and driving velocity in the saturated fine sand stratum, are evaluated. The results show that during shield tunneling under a diagonal urban river embankment, the additional stress and asymmetrical load effects should be considered, and the shield slurry pressure and jacking thrust should be adjusted according to the distance between the cutter head and the embankment. Furthermore, based on settlement monitoring data, the driving velocity of the shield should be reasonably adjusted in a timely manner to avoid disturbing the fine sand stratum below the embankment.
In deep rock engineering, the rock mass can be subjected to thermal stress caused by sudden changes in temperature, which is referred to as thermal shock (TS). To study the effect of TS on heated ...sandstone, three cooling methods are used to provide different cooling rates. Then the coupled dynamic and static loading tests are carried out on the heated sandstone by means of a modified split Hopkinson pressure bar (SHPB) system. The test results show that as the heating level increases, the dry density, P-wave velocity, and the dynamic combined strength of the heated sandstone decrease, while specimen porosity increases. Particularly, a sharp change in the physical properties of sandstone can be observed at 650 °C, which is believed to be caused by the α-β transition of quartz at 573 °C. At each heating level of the test, the damage caused by the higher cooling rate to the heated sandstone is more than that caused by the lower cooling rate. The different failure modes of sandstone with increasing temperature are analyzed. The mechanism of TS acting on heated sandstone is discussed, and two typical fracture patterns reflecting the action of TS are identified through SEM.
Many natural and engineered granular materials consist mainly of irregular-shaped non-spherical particles. In this work, a novel Fourier series-based Discrete Element Method (FS-DEM) is developed for ...the computational mechanics of irregular-shaped particles. In FS-DEM, Fourier series-based particle geometric description and coordinate representation are introduced, where particle shapes are implicitly determined by FS coefficients, which remain constant and are independent of particle positions or kinematics. Using the FS-based particle representation, contact detection and resolution algorithms are then developed to identify contacts and resolve contact geometric features. The FS-DEM method is completed with recourse to conventional contact behavior, laws of motion, and movement integration. The accuracy and computational efficiency of the FS-DEM framework are evaluated via three numerical examples and compared with the Overlapping Discrete Element Cluster-based DEM method. Results demonstrate the robust and superior performance of the FS-DEM method and its potential for efficient computational modeling of irregular-shaped particle systems.
•Novel FS-DEM framework for computational mechanics of irregular-shaped particles.•FS-based method for particle geometric description and coordinate representation.•New contact detection and resolution algorithms proposed.•Robust and superior performance demonstrated for single and multiple-particle systems.
•Thermal-plasticity-damage can be captured within a consistent and unified manner.•A more general equation of state in semi-logarithm space is proposed.•New hardening rules have been proposed through ...a unified consistent condition.•A new damage evolution law has been presented in this paper.•A temperature reduction function is proposed for brittle-ductile transition.
A coupled thermal-elastic-plastic-damage model for concrete subjected to dynamic loading is proposed. This model is formulated in the thermodynamic framework, with the adoption of critical state concept, bounding surface plasticity and continuum damage model (small strain being assumed). The contributions of temperature change, plasticity hardening/softening, damage evolution have been taken into account, with cross coupling effects among temperature, damage, strain rate and plasticity being considered through the consistent condition of thermodynamic model. Specifically, the variation of dynamic yield surface depends on the level of mean pressure, damage evolution, strain rate and plastic strain, which can be expressed through a general hardening law in bounding surface plasticity. The extension or contraction of dynamic bounding surface has been described by both compression and extension parts. For the consideration of higher strain rates and ultimately high pressures, the relationship between volumetric strain-mean pressure has been expressed through a more general equation of state (GEOS), which is different from traditional equation of state (EOS) under impact loading. This model has been validated through modelling extensive experimental results in literature, with good agreement among modelling results and experimental data being achieved. All model parameters are measurable physical entities and can be calibrated through conventional experimental approach or taken from literature.
•A detailed FDEM numerical method to simulate mechanical and fracturing responses of heterogeneous geomaterials with irregular inclusions is systematically developed.•A computational geometry method ...named CWSVM is proposed to control mesh quantity and quality.•A signed-distance-field-based discrete element method (SDF-DEM) is employed to approach the natural allocation and orientation of inclusions.•A combined constitutive model is proposed to consider the shearing hardening behaviour for the cohesive elements.•Effects of the interface strength on the mechanical and fracturing behaviours of inclusion-containing geomaterials are extensively discussed.
In this paper, a detailed FDEM approach to simulate the mechanical and fracturing responses of heterogeneous geomaterials with irregular inclusions is systematically developed. The inclusion surface morphology is first obtained through 3D scanning techniques. A computational geometry method, the curvature-weighted sphere Voronoi method (CWSVM), is adopted to control the mesh quantity and quality and ensure the efficiency and accuracy of the FDEM numerical model. A signed-distance-field-based discrete element method (SDF-DEM) is employed to approximate the natural distribution and orientation of inclusions. Heterogeneous geomaterials with large inclusion contents (such as 60% and 70%) are generated effectively and efficiently through this approach. Next, to model the fracturing process, a finite discrete element method (FDEM) model is developed by integrating cohesive elements into the mesh in a fast and efficient manner. In addition, a combined constitutive model is proposed to consider the shear-hardening behaviour of the cohesive elements. The proposed numerical approach is verified through comparison with experimental results, including the shape of inclusions and mechanical responses of geomaterials. The results demonstrate that both satisfactory precision and low calculation costs can be achieved using the proposed algorithm. The consequent simulation performance is verified through comparisons of observations and numerical results with experimental results for failure patterns and mechanical behaviours. In addition, the effects of the strength of the interfaces between the inclusions and matrix on the mechanical and fracturing characteristics of inclusion-containing geomaterials are analysed quantitatively. The mechanical strength decreases rather than increases with increasing content of inclusions when the interface strength is less than the matrix strength.
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The discrete element method (DEM) has become a prominent tool for modeling granular media, whereas the development of versatile and efficient particle models for the modeling of ...irregular-shaped particles remains a heated topic and challenge. In this work, a new particle model based on polybézier curves to describe particle shapes is proposed for the modeling of smooth and irregular-shaped particles. In particular, cubic bézier curves are adopted because they have a fairly high degree of freedom in modeling curved geometries as well as a closed-form support function. With the particle geometry and support function derived from cubic polybézier curves, the Gilbert-Johnson-Keerthi algorithm is adopted to detect contacts, and the expanding polytope algorithm is adopted to resolve contact geometric features. To generate polybézier-based particle templates from images of particle shapes, a particle swarm optimization-based geometric fitting procedure is also developed. The effectiveness of the proposed particle model for shape representation is validated using a chart of particle shapes with various roundness and sphericity characteristics. DEM simulations of random packing and biaxial compression tests on polydispersed irregular-shaped particles are also presented, and the results show that the proposed model has fairly good computational efficiency and numerical stability.
•A system is proposed to obtain heterogeneous rocks with irregular inclusions.•Realistic inclusion geometry is obtained and controlled by combining the circular parameterization and Fourier ...transformation.•An unique overlapping detection algorithm based on level-set function is developed to allocate inclusions.•Hydraulic fracturing are captured by integrating cohesive pore pressure elements into traditional finite element model.•A systematic hybrid finite-discrete approach for investigating hydraulic fracturing of heterogeneous rocks is proposed and validated.
A systematic hybrid approach for modelling the hydraulic fracturing process of heterogeneous rocks with irregular inclusions is developed. This approach is based on a series of computational algorithms, including Fourier series transformation, level-set-based overlapping detection, and the finite-discrete element method. Three major steps are included: (1) circular parameterization and Fourier transformation are employed to reproduce realistic inclusion contours with arbitrary irregular shapes; (2) a novel overlapping detection method based on a level-set function is employed to allocate irregular inclusions effectively and efficiently; and (3) the finite-discrete element model is established by integrating cohesive elements with pore pressure nodes into the solid mesh to simulate the progressive hydraulic fracture and interface crack of heterogeneous rocks. To validate the proposed hybrid approach, modelling results by the established model are compared with numerical simulations in the literature. In addition, the influences of injection speed and interface strength on the mechanical and fracturing responses of heterogeneous rocks are discussed. The results demonstrate that the proposed hybrid approach is capable of simulating the hydraulic fracturing process of heterogeneous rocks.
It is challenging to model granular particles with arbitrary shapes and related complications to fluid–particle interactions for granular flows which are widely encountered in nature and engineering. ...This paper presents an improved framework of the immersed boundary method (IBM)-based fully resolved computational fluid dynamics (CFD) and discrete element method (DEM), with an emphasis on irregular-shaped particles and the implications to particle–fluid interactions. The improved CFD-DEM framework is featured by two novel enhancements with signed distance field (SDF). First, an SDF-based formulation is employed to enable handling of granular particles with arbitrary shapes in DEM robustly and efficiently. Second, the IBM is modified to be consistent with SDF to fully resolve fluid–particle interactions in the presence of non-spherical particles. Such treatments leverage SDF as a generic interface to furnish a new SDF-CFD-DEM framework for universal modeling of arbitrarily shaped particles interacting with multiphase fluids with desired resolutions. Exemplified particle shape models include super-quadrics, spherical harmonics, polyhedron and level set, and new shape models can be flexibly developed by implementing the unified SDF-based shape interface. The proposed SDF-CFD-DEM is validated and showcased with examples including particle settling, drafting–kissing–tumbling, immersed granular collapse, and mudflow. The results demonstrate the good accuracy and robustness of the SDF-CFD-DEM and its potential for efficient computational modeling of multiphase granular flows involving granular particles with arbitrary shapes.
This work proposes a centroidal Voronoi tessellation (CVT)-based site investigation scheme, which is applicable to arbitrary site geometries and arbitrary numbers of investigation locations. A ...modified Lloyd algorithm is developed to generate CVT-based site investigation programs. With the data from prior site investigations, the random field statistics of a site property are estimated using a Markov chain Monte Carlo simulation-based Bayesian inference approach, and the site property at each location is estimated using Kriging interpolation. The performance of the CVT-based site investigation programs and optimization are demonstrated using two illustrative examples, namely, a square site and an irregular site.
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